1. Field of the Invention
The present invention relates to a method of applying image data as a visually detectable pattern with at least one embedded data element at an optical record carrier.
The present invention further relates to an apparatus for applying image data as a visually detectable pattern with at least one embedded data element at an optical record carrier.
The present invention still further relates to an optical record carrier having applied thereon image data in the form of a visually detectable pattern with at least one embedded data element.
2. Related Art
A visually detectable pattern comprises for example a logo, a sequence of characters or a combination thereof. The visually detectable pattern is printed at a resolution suitable for detection by the human visual system. For example the visually detectable pattern may be printed at a resolution of 1 to several hundreds dots per mm2 (as compared to computer readable data, which is stored at the record carrier at a resolution in the order of several Mbits/mm2). In this way, a user does not need a reading device to recognize the contents of the optical disk, but a simple visual inspection suffices. Such a visually detectable pattern can also serve as a means to detect the authenticity of the record carrier.
It is desired that the visually detectable pattern is applied at the side of the record carrier that also accommodates the regular data, to facilitate that the visually detectable pattern can be applied by the same means as such regular data.
A method and a device for providing a watermark at a record carrier is disclosed in EP 1,710,896. According to the method described therein, a parameter of the channel code is controlled to introduce a predetermined run-length distribution. In particular said parameter is the choice of the merging bits used in the channel code. Although this results in a visually detectable pattern, the contrast is very weak. There is a need to apply a visually detectable pattern at an optical record carrier having a reasonable contrast while allowing data to be embedded in the visually detectable pattern.